Corrugated aluminium tube and electric cable employing the same as a sheath



Dec. 24, 1957 J. R. PENROSE 2, 7,

CORRUGATED AL INIUM TUBE AND ELECTRIC CABLE v EMPLOYING THE SAME AS ASHEATH 2 Sheets-Sheet 1 Filed Oct. 30, 1953 FIG.

ALUMINIUM P=O-35 to 0-455 CORRUGATED ALUMI NIUM TUBE AND ELECTRIC CABLEDec. 24, 19 57 J R. PENROSE 2,8 7,

EMPLOYING THE. SAME AS A SHEATH 2 Sheets-Sheet 2 Filed Oct. 30, 1953 Rfrom 0-1110 to 043 D T fr6m O'O3 D to 0-040 d rrm 0920" t 0-84 :1

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I Q I l d from O-Q2D t0 084D D l F I G 4- from 035D \Llp/[S W n 5L.PEIQROSE INV NTOR y 04L ATTORNEY United States atent O M CORRUGATEDALUMINIUM TUBE AND ELEC- gRlC CABLE EMPLOYING THE SAME AS-A HEATH,

JamesRon-ald Penrose, Watford, England, assignor to Pirelli-General'C'able Works Limited, London, England, a British company ApplicationOctober 30, 1953, Serial No. 398,856

Claims priority, application Great Britain October 31, 1952 Claims. (Cl.138--50) I The present invention relates to-a corrugatedaluminium tubeand to electric cables employing the. same as a sheath, the corrugationsbeing disposed circumferentially or helically.

It has been proposed to provide an electric cable with a corrugatedsheath of aluminium or aluminium alloy, the sheath being manufactured bysurrounding the core of the cable with a tube and subsequentlyperforming a corrugating operation which may be arranged to bring thetroughs of the corrugations into contact with the cable core. The tubeon which the corrugating operation is performed to make the sheath may,if desired, be manufactured by welding the edges of a strip or strips ofmaterial to form a tube surrounding'the core of the cable.Alternatively, the core of the cable may be threaded into a preformedlength of tube.

When attempts were made in the past to manufacture such cables,difficulties were experienced, when the cable with the corrugated sheathwas subjected to bending tests, by reason of the formation of cracks,especially near the roots or crests of the corrugations, these defectsappearing after repeated reversed bending of the cable. We have foundthat, with cables sheathed with aluminium or soft aluminium alloys, theability of the cable sheath to withstand such reversed bending tests canbe improved by selection of the pitch of the corrugations and the depthof corrugation in relation to the diameter of the sheath. It is to benoted that, throughout this specification, the term pitch designates thespacing of the crests of the corrugations axially along the cablesheath, whether such corrugations lie in planes strictly at right anglesto the sheath axis or are helical in form. It is, of course, necessarythat the depth of corrugation should be sufiicient to ensure that, whensubjected to the bend test, which may, for example, be performed arounda radius equal to six times the overall diameter of the sheath, thecorrugations on the outside of the bend are not completely flattened.

According to the present invention, in an electric cable having acircumferentially or helically corrugated sheath of aluminium or a softaluminium alloy, the exterior root diameter of the corrugations isarranged to lie between 0.92 and 0.84 of the exterior crest diameter ofthe sheath and the pitch of the corrugations is arranged to be between0.35 and 0.45 of the exterior crest diameter of the sheath.

Corrugations of the required contour and pitch, as above defined, areconveniently produced by the use of one or more corrugating toolsarranged to exert pressure on the exterior of the cable sheath.Preferably the radius of the working portion of the corrugating tool, orof each of them as the case may be, is of the order of one eighth of theexterior crest diameter of the sheath.

If the sheath, when incorporated in the cable, is to be capable ofwithstanding, without damage, a test such as that above mentioned,namely repeated bending around a radius equal to six times the overalldiameter of the sheath, its wall thickness may advantageously be between2,817,363 Patented Dec. 24, 1957 0.03 and 0.04 of the exterior crest oroverall diameter of the sheath. If, however, such a stringent test benot required, for instance, if the bending radius be enlarged to tentimes the exterior crest diameter, a thinner sheath may be employed. Insuch cases the wall thickness may be 0.03 of'the exterior crest diameter+0.01 inch; in respect of cables havinga sheath of not less than 1 inchoverall diameter, this would result in a wall thickness lying withinthe. above limits.

I have found it particularly advantageous to arrange the corrugatingtool so that the exterior crest diameter of the corrugated sheath-issubstantially equal to the exterior diameter of the tubular sheathbefore corrugation. Also, if there is any material reduction in theexterior diameter of the sheath as a result of corrugation, this isanindication that excessive work has been performed on the. sheath,resulting in thickening of its wallparticularly at or near the roots ofthe corrugations.

One method according to the present invention of manufacturing acorrugated cable sheath will now be described by way of example withreference to the accompanying drawings in which:

Fig. l is a perspective view of the corrugating tool;

Fig. 2' is an enlarged view partly in longitudinal section showingapieceof the corrugated sheath;

Fig. 3' is an enlarged view in full longitudinal section showing apieceof the corrugated sheath Without the internal. core, said corrugationsbeing shown as helical; and

Fig. 4 is an enlarged view in full longitudinal section showing a pieceof the corrugated sheath. without the internal cable, said corrugationsbeing shown as circumferential and non-helical.

A strip of soft aluminium is progressively bent to surround a cable coreand thus form a sheath for the core and the edges of the strip arewelded together, preferably using a two-phase argon shielded electricarc with tungsten or tungsten base electrodes so as to form a weldedsheath 10. The sheath 10 is then subjected to a corrugating operation bymeans of a rotating corrugating tool carried by a housing 11 and havingfour rollers 12, 13, 14 and 15 carried by a face plate 16 which isarranged to rotate around the axis of the sheath 10. The face plate 16has four radial slots such as 17 engaged by bolts (not shown) securingbrackets such as 18 carrying spindles such as 19. The brackets 18 areadjustable radially. The roller 12 acts as a corrugating roller whilethe other rollers 13, 14 and 15 support the sheath 10. The face plate 16is driven at the requisite speed in relation to the speed of movement ofthe sheath 10 to produce the desired pitch of corrugation. The depth ofcorrugation can be set by radial adjustment of the roller 12.

As shown in Figure 2, the depth of the corrugation is set so that theexterior root diameter A of the corrugated sheath lies between 0.92 and0.84 of the exterior crest diameter B, which is not substantially lessthan the exterior diameter D of the uncorrugated sheath 10. The pitch ofthe corrugations P is arranged to be between 0.35 and 0.45 times theexterior crest diameter of the corrugated sheath. The thickness T of thematerial used for forming the sheath is preferably between 0.03 and 0.04of the exterior crest diameter B of the corrugated sheath.

I have found that the radius R of the working edge of the corrugatingroller 12 to form the corrugations having rounded roots and crestsshould be of the order of one eighth of the exterior crest diameter B ofthe corrugated sheath. I have found, however, that using a corrugatingtool as above described in which a plurality of rollers are arranged toexert comparatively local pressure on the portions of the tubular sheathwhich are to become the troughs of the corrugations, it may bedesirable, in order to ensure a smooth transition from the periphery ofthe roots to the periphery of the crests of the corrugations, that wherethe depth of the corrugation approaches the maximum above mentioned, theradius of the corrugating tool should be reduced somewhat, say to 0.11times the exterior crest diameter, while towards the minimum depth ofcorrugation the radius of the corrugating tool should be increasedsomewhat to, say, 0.13 times the exterior crest diameter. Bearing thisin mind, however, a given size of sheath can be corrugated to somewhatdifferent depths if desired.

While one embodiment of the present invention has been described asapplied to the manufacture of a sheathed electric cable using acorrugating tool having a plurality of rollers which are arranged toform a helical corrugation as shown in Figs. 1-3, it will be appreciatedthat the principles of the present invention can also be applied to themanufacture of sheathed electric cables using other suitable forms ofcorrugating tool, which may for instance, produce corrugations which arestrictly circumferential as shown in Fig. 4. Alternatively, a sheathhaving preformed corrugations, of contour and pitch according to thepresent invention, may be employed.

In the following claims the term aluminium is to be regarded asincluding soft aluminium alloys.

What I claim and desire to secure by Letters Patent of the United Statesis:

1. In an electric cable having a core, a sheath of aluminium for saidcore, said sheath being produced from plain tubing and having formedtherein encircling c0rrugations transverse to its length, the exteriorroot diameter of the corrugations being between 0.92 and 0.84 of theexterior crest diameter of the corrugated sheath, said exterior crestdiameter of the sheath being substantially equal to the exteriordiameter of the plain tubing and the pitch of the corrugations being0.35 to 0.45 times the exterior crest diameter of the corrugated sheath.

2. An article as set forth in claim 1 wherein the radius 4 ofcorrugation of the aluminium sheath in a plane which includes the sheathaxis is between 0.11 and 0.13 times the exterior crest diameter.

3. An article as set forth in claim 1 wherein the thickness of the wallof the corrugated aluminium sheath is between 0.03 and 0.04 times theexterior crest diameter of said sheath.

4. An article as set forth in claim 1 wherein the sheath has a diameterless than one inch and wherein the thickness of the wall of said sheathis 0.03 times the exterior crest diameter of said sheath plus 0.01 inch.

5. A corrugated aluminium tube produced from plain tubing and havingformed therein encircling corrugations transverse to its length, theexterior root diameter of the corrugations being between 0.92 and 0.84of the exterior crest diameter of the corrugated tube, said exteriorcrest diameter of the tube being substantially equal to the exteriordiameter of the plain tubing and the pitch of the corrugations being0.35 to 0.45 times the exterior crest diameter of the corrugated tube.

References Cited in the file of this patent UNITED STATES PATENTS798,448 Pogany Aug. 29, 1905 2,121,942 Barret June 28, 1938 2,365,181Fentress Dec. 19, 1944 2,606,953 Weston Aug. 12, 1952 2,614,607 KleinOct. 21, 1952 FOREIGN PATENTS 55,042 Germany Feb. 4, 1891 OTHERREFERENCES Publication 1, Horn & Ramsey, Bell System Cable SheathProblems and Designs, A. I. E. E. Tech. paper 51-330, August 1951 (page9 relied on).

1. IN AN ELECTRIC CABLE HAVING A CORE, A SHEATH OF ALUMIMIUM FOR SAIDCORE, SAID SHEATH BEUNG PRODUCED FROM PLAIN TUBING AND HAVING FORMEDTHEREIN ENCIRCLING CORRUGATIONS TRANSVERSE TO ITS LENGTH, THE EXTERIORROOT DIAMETER OF THE CORRUGATIONS BEING BETWEEN 0.92 AND 0.84 OF THEEXTERIOR CREST DIAMETER OF THE CORRUGATED SHEAT SAID EXTERIOR CRESTDIAMETER OF THE SHEATH BEING SUBSTAN TIALLY EQUAL TO THE EXTERIORDAIMETER OF THE PLAIN TUBING AND THE PITCH OF THE CORRUGATIONS BEING0.35 TO 0.45 TIMES THE EXTERIOR CREST DIAMETER OF THE CORRUGATED SHEATH.